The present invention relates to visual inspection of surfaces of articles, and more particularly to an illuminator for the automated optical inspection of ball grid array substrates, lead frames and printed circuit boards.
Apparatus and methods useful for illuminating substantially flat patterned surfaces of articles, such as electrical circuits on printed circuit boards (PCBs), ball grid array substrates (BGAs) reticles, semiconductors and other similar articles, during the automated optical inspection thereof are well known in the art.
During automatic optical inspection of flat patterned surfaces of articles, such as electrical circuits on PCBs and BGAs, the surface is illuminated by intense broad spectrum illumination while the article is transported beneath a sensor, such as a CCD or TDI camera. Conventionally, the sensors acquire scanned gray level images of the surface. Various materials which appear on the surface of an article each have different reflective properties and reflect illumination at a different level of intensity. For example, copper which defines conductors, various metal platings on the conductors, and the substrate itself each have different reflective properties. The reflected intensities in the image are sensed and automatically processed and analyzed to determine the presence of defects in the patterns on the surfaces.
The surfaces of electrical circuits being inspected, although substantially flat, generally exhibit a topographical relief that results both from the cross-sectional configuration of conductors as well as the surface microstructure thereof Typically, very intense illumination impinging on a surface of an article being inspected over a solid angle of incidence is employed to mitigate negative affects of the topographical relief
The following patents are believed to represent the state of the art in high intensity illumination for the inspection of substantially flat patterned article surfaces such as electrical circuits on printed circuit boards (PCBs), ball grid array substrates (BGAs), lead frames, reticles and semiconductors:
U.S. Pat. No. 4,421,410 to Karasaki describes an illuminator comprising a half reflecting mirror disposed above a printed wiring board. Concentrated light is reflected off the mirror and directed onto the wiring board at an angle substantially normal to the surface of the board and diffuse light emanating from fiber optics is simultaneously directed onto the surface at a large angle of incidence. An image of a line on the surface is transmitted through the mirror to a sensor.
U.S. Pat. No. 4,877,326 to Chadwick describes a high intensity illuminator providing focused quasi lambertian illumination to a region of the surface of an article to be inspected. The illuminator includes a half reflecting mirror, first and second and third elliptical cylindrical reflectors and first, second and third lamps, all having mutually parallel elongate axes. Two of the reflectors and two of the light sources are spaced from each other and illuminate the surface with focused light at a large angle of incidence. The half reflecting mirror, the third reflector, and the third lamp are arranged to reflect focused light along an axis normal to the surface to fill the gap between the first and second reflectors. Each lamp is located at one focus of a reflector, and the illuminated region is located at the second focus of the reflectors. Forth and fifth planar reflectors are provided at the longitudinal ends of the first, second and third reflectors, and a sensor is provided to image the illuminated region by sensing light reflected therefrom which passes through the half reflecting mirror.
Israel patent 81450 in the name of Orbotech Ltd. describes a high intensity illuminator similar in structure to that described in U.S. Pat. No. 4,877,326, but employing light supplied via fiber optics, and effectively having a numerical aperture substantially smaller than the numerical aperture of the apparatus described in U.S. Pat. No. 4,877,326.
U.S. Pat. No. 5,058,982 to Katzir describes a high intensity illuminator comprising a beam splitter cube and first, second and third elliptical cylindrical reflectors, two of which are spaced from each other. Light received via fiber optics is provided at one focus of each reflector. The reflectors are oriented so that the second focus of each reflector illuminates a region of a surface to be inspected. A third illuminator and a condensing lens are provided and oriented to direct light through the beam splitter and onto the surface to be inspected along an axis normal thereto. A sensor is oriented to receive light reflected from the surface via the beam splitter cube.
U.S. Pat. No. 5,153,668 to Katzir describes an illuminator for illuminating an area to be inspected on the surface of an article, in which the illumination is configured to be substantially circularly symmetric over a solid angle around an optical axis normal to the surface. A sensor is provided to image the surface through a gap between the illuminators.
U.S. Pat. No. 4,801,810 to Koso describes an elliptical reflector, comprising approximately one half of an elliptical cylinder, which is used to illuminate the surface of a printed circuit board. The axis of the elliptical cylinder is oblique to the surface of the printed circuit board. A lamp is disposed under the reflector at one focus of the ellipse, while the region illuminated is located at the other focus. An imaging system images the illuminated region through an aperture formed in the reflector.
The illuminator employed in Inspire(trademark) automated optical systems manufactured and sold by Orbotech Ltd., and described in copending PCT application PCT/IL98/00285 (unpublished), is a high intensity illuminator comprising a first light source that emits light over a continuous wide angle of illumination toward a surface of an article to be inspected and has a blocking element that blocks a portion of the continuous angle of illumination to form two separate portions of illumination. A second light source is employed to supply illumination to the region blocked by the blocking element. Concentrating optics are provided to concentrate the illumination onto the article. The illumination is provided at a first angle to the normal, and an imaging sensor is provided to image the illuminated region of the article at a second angle to the normal.
Systems which image a surface to be inspected along an imaging axis that is normal to the surface being inspected typically employ at least three separate sources of illumination. In systems that employ less than three sources of illumination to provide an intense solid angle of illumination, the surface is imaged along an axis which is oriented at a non-normal angle thereto.
Additionally, conventional systems that illuminate and image a surface to be inspected along an axis that is normal to the surface being illuminated acquire images via beam splitting apparatus that introduces undesired aberrations into the image.
The present invention generally seeks to provide high intensity illumination for the automated optical inspection of patterned articles in which two light sources together provide a solid angle of illumination, the spatial uniformity of which is adjustable.
One aspect of a preferred embodiment of the invention provides illumination of a region on the surface of an article over a solid angle using two independently adjustable sources of illumination, wherein the axis of at least one source of illumination is substantially normal to the surface. Preferably, the region illuminated is imaged by a sensor whose axis of imaging is also substantially normal to the surface.
According to another aspect of a preferred embodiment of the invention, a region of an article to be inspected is illuminated with a first illuminator, including a reflective surface which is apertured at a location which overlies the region to be inspected. Supplemental illumination of the region is provided through the aperture and a sensor images the region to be inspected by sensing light reflected therefrom through the aperture.
According to still another aspect of a preferred embodiment of the invention, an imaging system is provided in which the surface of the article is illuminated by a solid angle of illumination to illuminate a line, and wherein a sensor is provided to image the illuminated region in a manner that avoids transmitting reflected light from the region through a beam splitter or through a partially reflected mirror en route to the sensor.
Preferably, a partially reflective planar mirror is oriented along an imaging axis normal to the surface. Illumination is transmitted through the partially reflective planar mirror to provide illumination along an axis normal to the surface. Light reflected from the surface is reflected by the partially reflective mirror into the sensor for imaging the surface.
In accordance with still another aspect of a preferred embodiment of the invention, an illuminator is provided to illuminate a linear region along a surface of an article during automated optical inspection thereof. The illuminator is configured to provide a broad angle of illumination from a multiplicity of illumination sources. At least one illumination source provides illumination along an axis which is substantially normal to the surface. Illumination from that source is passed through an optical element that introduces astigmatism into the illumination along an axis of astigmatism that is substantially colinear to the linear region, thereby smearing the illumination along the illuminated linear region.
Another aspect of a preferred embodiment of the invention provides an illuminator for illuminating a linear region along a surface of a substrate with a broad angle of illumination. The illumination is provided by a plurality of sources, wherein a first source of illumination provides illumination along an axis that is substantially normal to the surface of an article. The illumination provided by the first source is passed through an optical assembly configured to introduce astigmatism into the illumination provided by the first source. The astigmatism is oriented along an axis that is substantially colinear to the linear region being illuminated. Preferably, an imaging sensor is provided to image the linear illuminated region at least partially along an axis that is normal to the surface of the article.
According to still another aspect of the invention, there is provided a substantially telecentric imaging system for imaging a region of a surface of an object during automated optical inspection thereof The system comprises a plurality of lenses and sensors operative simultaneously to acquire a plurality of images of mutually overlapping regions. Preferably, the maximum angle at which any pixel is imaged is less than approximately 5xc2x0 and preferably less than 3.7xc2x0 to the normal with respect to the surface. The imaging path of at least one of the sensors is preferably folded by a folding mirror which is located in a region adjacent to a waist in the imaging paths of the other sensors.
According to another aspect of the invention, there is provided an inspection system for automatically inspecting patterned articles. Illumination in a first spectral range is provided on one surface of the article and illumination in a second spectral range, distinguishable from the first range, is provided on the opposite surface of the article. Sensors are employed to sense the intensity of reflected light in the first spectral range, and to sense the intensity of transmitted light in the second spectral range. Patterns on the surface of the article are inspected based on reflected light intensity in the first spectral range. The presence and pattern of desired and undesired apertures in the article are inspected based on transmitted light in the second spectral range.
There is thus provided in accordance with a preferred embodiment of the present invention an illumination system including at least one reflector subtending an angle with respect to a location on a surface of an article, and first and second light sources, the first and second light sources each providing a light output, the light outputs from both of the first and second light sources being directed to impinge on the location on the surface of an article within the angle, at least one of the light outputs being reflected by the reflector.
Further in accordance with a preferred embodiment of the present invention the reflector is formed with a light transmissive region to permit a light output from a first one of a the first and second light sources to pass therethrough. Preferably the light transmissive region is an aperture formed in the reflector. Preferably the illumination system also includes an optical element disposed intermediate the first one of the first and second light sources and the aperture for directing the light output of the first one of the first and second light sources through the aperture. Additionally the optical element also includes at least one reflecting surface.
Alternatively the illumination system may also include an optical assembly disposed along an optical path extending between the optical element and the location on the surface of an article for directly light reflected from the location on the surface of an article to a light sensor. Preferably the optical assembly is generally transmissive to the light output of the first one of the first and second light sources directed through the aperture onto the location on the surface of an article and generally reflective of light reflected from the location on the surface of an article.
Furthermore the illumination system may also include a reflective surface disposed intermediate a second one of the first and second light sources and the reflector for directing the light output of the second one of the first and second light sources onto the reflector.
Additionally in accordance with a preferred embodiment of the present invention the at least one reflector is an elliptical reflector and the second one of the first and second light sources and the location on the surface of an article are each located at or near a locus of the elliptical reflector. Preferably the at least one reflector includes two spaced apart reflectors which together define a section of an ellipse. The spaced apart reflectors are preferably separated by an aperture.
Alternatively the first and second light sources may also be independently controllable light sources.
There is also provided in accordance with a preferred embodiment of the present invention an illumination system including a cylindrical reflector extending along a first longitudinal axis and having an axial aperture formed therein which extends along the longitudinal axis, a first elongate light source extending along a second longitudinal axis, generally parallel to the first longitudinal axis and being arranged to illuminate the cylindrical reflector, such that light from the first elongate light source is directed onto a plane generally along a third longitudinal axis, generally parallel to the first and second longitudinal axes, a second elongate light source extending along a fourth longitudinal axis, generally parallel to the first, second and third longitudinal axes, the second elongate light source being arranged with respect to the axial aperture of the cylindrical reflector such that light from the second elongate light source is directed through the axial aperture onto the plane generally along the third longitudinal axis, and an optical element disposed along a light path between the second elongate light source and the plane and being operative to pass light from the second elongate light source to the plane and to reflect light from the plane to an optical sensor.
Further in accordance with a preferred embodiment of the present invention the first elongate light source comprises an elongate light generating element and an elongate reflector extending along a fifth longitudinal axis, generally parallel to the first, second, third and fourth longitudinal axes and being operative to reflect light from the elongate light generating element onto the cylindrical reflector.
There is also provided in accordance with yet another preferred embodiment in accordance with a preferred embodiment of the present invention an illumination system including at least two elongate light sources extending along at least two light source longitudinal light source axes, each of the at least two elongate light sources being arranged to illuminate a plane generally along a longitudinal illumination axis, generally parallel to the at least two light source longitudinal axes, and an optical element disposed along a light path between at least one of the at least two elongate light sources and having astigmatism, the optical element being operative to cause light from the at least one of the at least two elongate light sources to be smeared along the longitudinal illumination axis.
There is also provided in accordance with another preferred embodiment of the present invention an illumination system including a light source arranged to illuminate an object, a plurality of lenses imaging light from the light source reflected by the object onto a plurality of light receivers, the physical sizes of the plurality of lenses and the spacing of the plurality of light receivers being such that the plurality of lenses cannot all lie in a single plane, folding optics arranged along light paths between the plurality of lenses and the plurality of light receivers and being arranged such that notwithstanding different physical separations between ones of the plurality of lenses and corresponding ones of the plurality of light receives the light paths between the ones of the plurality of lenses and the corresponding ones of the plurality of light receivers are substantially identical.
Further in accordance with a preferred embodiment of the present invention the plurality of lenses have substantially identical focal lengths.
Additionally or alternatively the plurality of lenses image at least partially overlapping regions on the object.
There is further provided in accordance with a preferred embodiment of the present invention an inspection device including first and second light sources arranged to illuminate a substrate having reflective features thereon, the first and second light sources providing light outputs having wavelength spectra which are at mutually distinguishable, and at least one light receiver receiving light from the first light source reflected from the substrate and receiving light from the second light source transmitted via the substrate.
There is further provided in accordance with a preferred embodiment of the present invention imaging apparatus including an illuminator illuminating a region on the surface of an article. A plurality of sensors is associated with a plurality of quasi-telecentric lenses, and the sensors and lenses are arranged to simultaneously image mutually overlapping portions of the illuminated region. Preferably, principal rays imaging each part of the portion deviate less than xc2x110xc2x0 from the normal, and more preferably they deviate less than or equal to 3.5xc2x0 from the normal.